Flat panel displays (FPD) such as liquid crystal displays (LCD) and organic electroluminescences (EL) and the like showing space saving and low powder consumption as compared with CRT, are widely spread as image planes of computers, televisions, portable telephones, car navigations or portable information ends. In FPD, various optical films are used for reflection reduction, wide viewing angle and the like. As such optical films, there are mentioned, for example, reflection reducing films such as antireflection (AR) films and the like which lower the surface reflection coefficient by an optical interference effect by making a multilayer structure composed of optical thin membranes of different refractive indices; polarizing films allowing permeation only of lights of specific vibration directions and blocking other lights; retardation films optically compensating colors of interference colors of LCD of STN mode, TN mode and the like; elliptic polarizing films obtained by integrating polarizing films and retardation films; wide-viewing-angle films which enlarge the visual field angle of LCD; and the like.
As the retardation film giving an optical compensation effect, a λ/4 plate is known. As one of optical properties of a retardation film, a wavelength dispersion property of retardation is known. Specifically, the wavelength dispersion property of a usual retardation film manifests a property of [Re(450)/Re(550)]>1>[Re(650)/Re(550)] (wherein, Re(λ) represents a retardation on a retardation film measured at a measuring light wavelength of λ nm). That is, the wavelength dispersion property of a usual retardation film is positive wavelength dispersion.
As the retardation film showing reverse wavelength dispersion, namely, a wavelength dispersion property of [Re(450)/Re(550)]<1<[Re(650)/Re(550)], a film of a mixture of two kinds of polymer A and polymer B is suggested using a polymer A and a polymer B of which difference between Re(450)/Re(550) when the polymer A is a retardation film and Re(450)/Re(550) when the polymer B is a retardation film is 0.05 or more, and specifically, films obtained by drawing the mixture are disclosed (Japanese Patent Application Laid-Open (JP-A) No. 2002-14234, [Claim 1], [0103], [0111], Examples 2 to 7). However, for changing the wavelength dispersion property, it is necessary not only to change the mixing ratio of the polymer A and the polymer B but also to change also the ratio of monomers used in a copolymer of the polymer A or the polymer B, and it is difficult to simply control the wavelength dispersion property, and additionally, a drawing process is also necessary for making a film. In general, polymers reveal poor mutual compatibility, thus, when they are mixed, there occurs problems of phase separation and increase in haze when optically observed.
Recently, with increase in the size of FPD, it has been clarified that when the whole display image plane is observed from wide angles, a display image is colored (called coloring phenomenon) and white and black are inverted (called inversion phenomenon), and when visual angle is inclined toward reverse visual angle direction which is an upper direction of a display image plane, there occurs a problem of decrease in contract. Optical films intending such wider visual field angle and higher display quality require improvement in visual field angle dependency and further improvement in the coloring phenomenon, in addition to the optical compensation effect and reflection reducing function. Further, since the wavelength dispersion property to be required varies depending on a difference in requirements in optical design of users and a difference in LCD mode, an optical film giving an arbitrary wavelength dispersion property is required.